Projection screen

ABSTRACT

A projection screen, having a projection surface formed of at least two segments, of which at least two segments are sound radiating segments capable of radiating sound waves from the projection surface and designed to reproduce different frequency ranges.

FIELD OF THE INVENTION

The invention relates to the design of projection screens, in particularof projection screens of a type that allow simultaneous reproduction ofsound.

BACKGROUND OF THE INVENTION

Presently, essentially two different types of projection screens exist:rear projection screens and front projection screens. With rearprojection screens, the image is produced on the side of the projectionscreen facing away from the spectator. This projection method is known,for example, from television picture tubes.

With front projection screens, the image is produced on the side of theprojection screen facing the spectator, whereby the images to bereproduced are projected on to the projection plane from a projectorplaced at a distance from the projection screen. This method, which alsoforms the subject matter of the present invention, is known, forexample, from movie theaters and slide projection. The latter (front)projection screens have a relatively large size as compared to the rearprojection screens described first. Movie theaters, for example,typically employ projection screens having a projection screen diagonalin excess of 15 meters.

If sound effects are to be reproduced in addition to the visual effects,then both projection methods rely on conventional loudspeakertechnology, wherein respective loudspeakers or loudspeaker boxes arearranged along the periphery of the respective projection screen. Thisdevice is necessary in order to convey to a spectator the impressionthat the respective sound events originate from the events displayed onthe projection screen or are at least related to these events.

To provide an adequate audio level for the room in front of large formatprojection screens, a large number of conventional loudspeakers ofsuitable signs should be provided. However, such sound-producing devicescan achieve excellent sound reproduction with setups having relativelysmall projection walls only if the space and/or area used for soundreproduction is disproportionately large relative to the size of theprojection screen and/or the size of the image. This is less of an issuewith relatively large projection screens. However, with projectionscreens having a large image diagonal, the audio effects can benoticeably misaligned relative to the visual effects, when the soundreproducing device is placed along the sides of the projection screen.Conversely, while placing the sound reproducing system behind theprojection screen improves the mutual correlation between visual andaudio effects for large projection screens, the projection screen candisadvantageously interfere with the reproduction of the highfrequencies.

For example, U.S. Pat. No. 5,025,474A discloses a projection screenconsisting of several segments of which at least some segments operateas sound radiating elements for radiating sound waves from theprojection plane of the projection screen. Similar projection screensare described also in U.S. Pat. No. 1,817,630 A, GB 353 439 A, EP 0 323110 A and U.S. Pat. No. 5,007,707 A. However, these arrangements stilldo not adequately reproduce high frequencies.

It is therefore an object of the invention to provide a projectionscreen which eliminates the disadvantages in the sound reproductionassociated with the aforementioned conventional devices.

A very compact and space-saving device for simultaneous transmission ofvisual and audio effects includes a projection wall with at least onesegment that radiates sound waves out of the projection plane of theprojection screen. With this device, the required area and/or space isno greater than the size of the respective projection screen; inaddition, the visual and audio events are once more combined in a singleplane and completely and correctly associated with each other.

This is achieved by designing the sound reproduction segments of aprojection screen with a different depth perpendicular to the projectionplane in order to optimize the reproduction of certain frequency ranges.

The tonal response is optimized by using the entire area for soundreproduction. The higher frequencies are also no longer attenuated bythe screen located in front of the loudspeakers.

If, the respective edges of the segments of the projection wall can bemutually decoupled by connecting elements, so that optimally formedsound reproduction segments for reproducing certain frequency ranges canbe integrated in the same projection screen and, in addition, regions orzones can be created for transmitting, for example, the differentchannel information in stereo.

A particularly simple decoupled connection between the segments can beobtained if the segments are made of a core layer and at least one coverlayer. The segments of the cover layer(s) and the core layer can then beconnected in a simple manner by having the respective cover layer and/orthe core layer also bridge the radial gaps between adjacent segments. Inparticular, by using the core layer to connect several segments,relatively large sections of the core layer can advantageously bemanufactured as a continuous uniform piece before the segments producedfrom this piece are decoupled through cutouts or milled-out portions inthe core layer.

The segments and/or sound radiating segments integrated in a projectionscreen do not necessarily require an area of uniform size in theprojection plane of the projection screen. Instead, these areas can bedesigned and associated with each other to provide flexibility in thesound reproduction of the projection screen.

The bass reproduction can be significantly improved by arranging thesegments that are optimized for reproducing low frequencies primarily inthe central region of the projection screen, because those segmentsand/or portions of the projection screen that laterally abut thesegments provided for the bass transmission, can be used to reducedipole shunting.

The sound reproduction can be further optimized by optimizing the soundproduction segments of a projection screen that are designed toreproduce certain frequency ranges, by giving them a different depthperpendicular to the projection plane.

The projection surface of the projection screen need not be planar, butcan also be curved. This device modifies the radiated sound pattern,thereby further optimizing the sound generation for the room. The—notnecessarily uniform—curvature of the projection surface selectivelyaddresses, for example, certain areas in the auditorium and hence canfurther improve the audio perception.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a projection screen;

FIG. 2 shows a top view of a projection screen;

FIGS. 3a-e show five different connections between segments of aprojection screen; and

FIG. 4 shows the backside of a projection screen.

DETAILED DESCRIPTION OF CERTAIN ILLUSTRATED EMBODIMENT

The invention will now be described in detail with reference to theFigures.

FIG. 1 shows a projection wall 10 formed of a plurality of segments 11.A projector 12 that projects images onto the projection plane 30 of theprojection screen 10 is placed at a distance from the front of theprojection screen 10. Depending on the application, the projector 12 canbe a slide projector, a film projector, an LCD projector or a laserprojector.

Each of the segments 11 depicted in FIG. 1 is formed as a soundradiating segment 11′. As described above with reference toDE-A-19757097.6, to which reference is made in the present application,each sound radiating segment 11′ is formed of a light core layer 13(FIG. 3a) and at least one cover layer 14 (FIG. 3a), wherein therespective cover layers 14 are made of a material having a particularlyhigh dilatational wave velocity and are connected with those surfaces ofthe core layer 13 having the largest area. For sake of completeness, itshould be mentioned that the respective sound radiating segments 11′ areprovided with, for example, electrodynamic transducers that producebending waves in response to control signals transmitted to the soundradiating segments 11′. Further details are described in theaforementioned reference.

By constructing the entire projection screen 10 of sound radiatingsegments 11′, the entire projection plane available for reproducing theprojected image is simultaneously available also for reproducing sound.As mentioned above, this arrangement not only saves space, but alsoallows the spectator to associate the audio and visual effects much morestrongly as compared to conventional setups. The spectator now has thefeeling that the audio events originate from the same location as theassociated visual event.

It should be pointed out that the screen 10 depicted in FIG. 1 thereincan have a slight curvature (not shown). This—concave—curvature isimplemented essentially by placing all regions of the projection screen10 substantially at the same distance from the point-like image source,i.e., the projector 12. When viewed from the front, the projection plane30 of the projection screen 10 has then the form of the open shell,which tends to more strongly concentrate the sound waves that aresimultaneously radiated from the projection screen 10. Conversely, ifthe sound waves are to be dispersed by the projection screen 10, thenthe projection screen 10 can have a convex curvature. The curvature ofthe projection screen 10 also need not be uniform over the entire areaof the projection screen. Instead, the projection screen 10 can have anumber of different radii of curvature.

The entire projection screen 10 depicted in FIG. 1 is provided withsound radiating segments 11′. In another embodiment (not shown),segments 11 which are not constructed as sound radiating segments 11′can also be integrated with the projection screen 10. Such (blind)segments 11 can be used to attach and support the projection screens 10at the respective installation location.

A second embodiment of a projection screen 10 is depicted in FIG. 2. Allsegments 11 are formed as sound radiating segments 11′; however, unlikethe embodiment of FIG. 1, the sound radiating segments 11′ of FIG. 2have areas of different size in the projection plane 30. The largestsound radiating segment 11′ is placed in the central portion of theprojection screen 10 and optimized for reproducing low frequency audioevents. A row consisting of six sound radiating segments 11′ which havethe respective smallest area in the projection plane and are employedfor radiating high frequency audio events are located at the upper andlower edges 15, 16 of the projection screen 10. A sound radiatingsegment 11′ that has an area with a size intermediate between theaforementioned sound radiating segments 11′ is located at the lateraledges 17, 18 of the projection screen 10 and used to reproduce audioevents in the midrange. For sake of completeness, it shall be mentionedthat the sound radiating segment 11′ for the bass reproduction need notnecessarily be located in the center of the projection screen 10. It isalso possible to reproduce low frequency sound by arranging in thecenter region of the projection screen 10 and/or across the entireprojection screen a plurality of not necessarily symmetricallypositioned sound radiating segments 11′. However, the (bass) segments11′ should also be surrounded, as previously described, by othersegments 11 or 11′ to prevent an acoustic short circuit. For the samereasons, the respective (bass) segment 11′ should also be connected toat least the adjacent segments 11, 11′ with connecting elements 19, 20that are impervious to sound waves.

The connection between the (blind) segments 11 and/or the soundradiating segments 11′ is illustrated in more detail in FIGS. 3a to 3 e.

FIG. 3a shows two core layers 13 arranged side-by-side, wherein a gap Aexists between the two core layer 13. The two surfaces of the twoillustrated core layers 13 that have the largest area, are connected bya respective cover layer 14. Since the upper and lower cover layer 14for both segments 11 (11′) is formed as a common cover layer 14, thiscover layers 14 simultaneously also forms a continuous bridge across thegap A, thereby decoupling the two segments 11 (11′). For sake ofcompleteness, it should be pointed out that the actual distance betweenthe two cover layers 14 and the respective surfaces of the core layers13 is smaller than shown in the drawings.

FIG. 3b shows two core layers 13 that are already provided with one ortwo cover layers 14 (not shown in FIGS. 3b). The gap A between thesegments 11 (11′) can be bridged while simultaneously acousticallydecoupling the segments from one another by gluing two strips 19 to thecover layers 14 of the core layers 13 to cover the gap A.

In another embodiment (not shown), the two strips 19 of FIG. 3b thatconnect the two segments 11 (11′) can also be glued directly on the corelayers 13, i.e., before the cover layers 14 are applied. In this case,the two cover layers 14 of both core layers 13 can be continuous—asdescribed above with reference to FIG. 3a—, so that the respectiveconnection between the two segments 11 (11′) consists of a strip 19 anda cover layer 14 covering the strip 19.

To give the surface structure in the embodiment depicted in FIG. 3b auniform appearance, the strips 19 can be inserted into milled-outsections (not shown) in the core layers 13, with the thickness of themilled-out sections being matched to the thickness of the strips 19.

Unlike the embodiment of FIG. 3b, in the embodiment depicted in FIG. 3cthe narrow sides 21 of the two core layers 13 are also connected with aconnecting element 20. The strips 19 in this case have essentially thepurpose of providing a uniform surface characteristics between twosegments 11, (11′).

FIG. 3d depicts two segments 11 (11′) with a uniform core region 13′.Unlike the core layers 13 depicted in FIGS. 3a-c and 3 e that areseparated by a gap A, the core layer region 13′ of FIG. 3d has twotrapezoidal milled-out portions 22 so as to reduce the thickness of thecore layer regions 13′ and promote a decoupling of the two segments 11(11′). Accordingly, the remaining portion between the two segments 11(11′) acts as a connecting elements 20 in the same fashion as theconnecting element 20 illustrated in FIG. 3c. The two segments 11 (11′)can also be covered with cover layers 14 that are uniform for bothsegments 11 (11′) and cover the milled-out portions 22.

FIG. 3e shows an additional embodiment of a connection between two(blind) segments 11 and/or sound reproduction segments 11′. Both sidesof the two core layers 13 are provided with cover foils 14. Forconnecting the two segments 11 (11′) with one another, one of the coverlayer 14 has a region 14′ that projects over the narrow sides 21 of thecore layer 13. These projecting regions 14′ of the cover layers 14 canbe used—as illustrated in FIG. 3e—to connect two segments 11 (11′) byconnecting the projecting region 14′ of one segment 11 (11′) with acover layer 14 of the other segment 11 (11′). When the segments 11 (11′)are formed as shown in FIG. 3e, large quantities of such segments 11(11′) formed of the core layer 13 and the cover layers 14 can easily bepre-produced and connected with one another through the projectingregions 14′.

For connecting two segments 11 (11′) located on both sides of the gap A,the respective segments 11 (11′) can also be provided with twoprojecting regions 14′. This situation is indicated in FIG. 3e for theright segment 11 (11′) by dotted lines.

With reference to the embodiments depicted in FIGS. 3a to 3 e, it shouldbe mentioned that the depicted connections between two segments 11 (11′)should be designed so as to be impervious to sound at least if one ofthe segments 11 (11′) attached in this manner is connected to a soundradiating segment 11′ used to reproduce low frequency sound. Only aconnection that is impervious to sound can reliably prevent acousticshort circuits.

It should also be noted that the connecting elements 19, 20, due totheir respective spring mass damping characteristics, operatesimultaneously as mechanical filters and can hence be used tointentionally optimize and/or control the sound radiatingcharacteristics.

FIG. 4 shows a rear view of a projection screen 10 formed of three soundradiating segments 11′. As seen in FIG. 4, the different sound radiatingsegments 11′ can not only have a different area, as described above withreference to FIG. 2, but can also have a different depth perpendicularto the projection plane 30 of the projection screen 10. The differentdepth of the sound radiating segments 11′ is used to optimize the soundreproduction of certain regions of the projection screen 10. If—as shownin FIG. 4—the different sound radiating segments 11′ are combined withone another in such a way that the sound radiating segments 11′ have adifferent depth only on the backside of the projection screen 10, thenthe front surface of the projection screen 10 (not visible in FIG. 4)remains uninterrupted to form a smooth projection plane 30.

We claim:
 1. Projection screen comprising a projection surface formed ofat least two segments, of which at least two segments are soundradiating segments capable of radiating sound waves from the projectionsurface and designed to reproduce different frequency ranges, wherein asound radiating segment that radiates sound waves in a lower frequencyrange has a smaller depth in a direction perpendicular to the projectionsurface than another of the sound radiating segments that radiates soundwaves in a higher frequency range.
 2. Projection screen according toclaim 1, further including connecting elements which connect edges ofthe at least two segments of a projection surface with one another in adecoupled fashion.
 3. Projection screen according to claim 2, wherein atleast the sound radiating segments are formed of a core layer having twomajor surfaces and at least one cover layer, wherein at least one coverlayer is connected with one of the major surfaces of the core layerpositioned in the projection surface, and wherein the respectiveconnecting elements are formed by at least one of the core layer and oneof the cover layers.
 4. Projection screen according to claim 1 whereinthe sound radiating segments are designed for different reproductionapplications, and the sound radiating segments having differentreproduction applications have different size areas in the projectionsurface.
 5. Projection screen according to claim 4, wherein a soundradiating segment essentially used for reproducing low frequencies isarranged primarily in a center region of the projection surface andsurrounded at least partially by the remaining segments.
 6. Projectionscreen according to claim 1, wherein at least the projection surfacethat faces a projector is curved.